<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>打分器</title>
    <script src="js/jquery.min.js"></script>
</head>
<body>
    <div class="box">
        <input type="text" id="a" value="0">
        <select name="请选择" id="symbol">
            <option value="0">+</option>
            <option value="1">-</option>
            <option value="2">*</option>
            <option value="3">/</option>
        </select>
        <input type="text" id="b" value="0">
        <input type="button" id="btn" value="=">
        <input type="text" id="c" value="">
    </div>
</body>
<script>
    $symbol = $('#symbol');
    $btn = $('#btn');
    $a = $('#a');
    $b = $('#b');
    $c = $('#c');

    $btn.click(function(){
        const a = parseInt($a.val());
        const b = parseInt($b.val());
        console.log(a);
        console.log(b);

        switch($symbol.val()){
            case '0':
                $c.val(a+b);
                break;
            case '1':
                $c.val(a-b);
                break;
            case '2':
                $c.val(a*b);
                break;
            case '3':
                $c.val(a/b);
                break;
        }
    })
</script>
</html>